What three Kryptonians were on Earth in 2006?

Question

I recently picked up a cheap back issue of Action Comics #842, dated October 2006. In it, a giant alien, the "Auctioneer," is menacing the Earth. He's mostly oblivious to the frantic human activity around him, but Superman manages to attract his attention. The alien is delighted to have found a Kryptonian, and instructs his equipment to scan the Earth for others. Superman overhears him comment that, in total, three were found, and is surprised, since the only other Kryptonian he knows about is Supergirl. However, the identity of the third Kryptonian is not revealed in that issue.

So, who was it?

Answer 1

According to Wikipedia, in Superman #669 it is revealed that the "Third Kryptonian" is in fact Superwoman (AKA Karsta Wor-Ul, AKA Kristin Wells)

In Superman: The Third Kryptonian, it is revealed that a third Kryptonian (that is, after Clark and Kara) is on Earth. It is explained that the third Kryptonian does not refer to Chris Kent (Superman's foster son, General Zod's biological child), Power Girl (an Earth-Two Kryptonian) or Krypto (a canine Kryptonian). The storyline introduces a new Kristin Wells, an older woman and Kryptonian survivor named Karsta Wor-Ul who had left the planet many years before its destruction.